1. Field of the Invention
The present invention relates to a dip-type substrate processing apparatus for chemically processing thin plate substrates (hereinafter referred to simply as "substrates") such as semiconductor substrates, and glass substrates for liquid crystal or photomask applications. The present invention also relates to a method of holding substrates in the dip-type substrate processing apparatus.
2. Description of the Background Art
In recent years, much progress has been made in development of carrier-less dip-type substrate processing apparatuses. In such apparatuses for chemically processing substrates, substrates directly held by a chuck of a substrate holding device are immersed in a plurality of successive processing baths, without the assistance of a carrier for carrying the substrates.
A carrier-less dip-type substrate processing apparatus, as the name connotates, does not include a carrier. This creates various outstanding advantages over a conventional substrate processing apparatus which employs a carrier, in terms of maintenance costs and processing ability. For instance, the carrier-less apparatus reduces the sizes of processing baths since no carrier is used, and hence, less processing fluid and less pure water are necessary. Due to these advantages of decreased maintenance costs and improved processing ability, carrier-less dip-type substrate processing apparatuses are enjoying wider use in the industry.
FIGS. 24 to 26 show conventional substrate holding devices used in this type of substrate processing apparatuses.
The conventional substrate holding device of FIG. 24 comprises a pair of chucks 1. The chucks 1 bend inward at their lower portions. Two pairs of holding poles 3 are attached to the inward bents 1a of the chucks 1 so that two holding poles 3 face the other two holding poles 3. The holding poles 3 are notched at equal pitches on their inward surfaces. Guide grooves 3a formed on the holding poles 3 are in longitudinal alignment with each other, and therefore, capable of holding substrates 2.
A processing bath 50 is filled with a processing fluid 51 and equipped with a support member 4. Supported by the support member 4, the substrates 2 stand on end in the processing bath 50.
Guide grooves 4a are formed on the top surface of the support member 4. Since the pitches of the guide grooves 4a are the same as those of the guide grooves 3a, the substrates 2 slid into the grooves 4a will be supported on end and nearly parallel to each other.
The holding action of the substrates 2 by the chucks 1 involves opening the chucks 1 sideways to such an extent that the lower pair of the holding poles 3 do not touch the rims of the substrates 2 and thereafter lowering the chucks 1 to a predetermined point. The chucks 1 are then closed to slide the lower rims of the substrates 2 into the guide grooves 3a of the holding poles 3, and are lifted up with the substrates 2 fit in the grooves 3a at the rims.
The conventional substrate holding device of FIG. 25 comprises chucks 5 which are provided with holding plates 6 in their substrate holding portions. Guide grooves 6a are formed on the inward walls of the holding plates 6 at equal pitches. Substrates 2 are held at their rims by the holding plates 6.
FIGS. 26A-26C show another substrate holding device of conventional style. A support member for supporting the substrates is formed by two holding poles 7, each having guide grooves 7a formed on their inward surfaces. The holding poles 7 are disposed parallel to each other. A vertical driving means (not shown) travels the length of holding poles 7 in a vertical direction. The apparatus further comprises three other holding poles 8 which have guide grooves 8a (FIG. 26C) notched on their inward surfaces. The holding poles 8 are disposed parallel to each other. A horizontal driving means (not shown) moves along the length of the holding poles 8 in a horizontal direction.
The two holding poles 7 are moved away from the position shown in FIG. 26A to the position shown in FIG. 26B. The three holding poles 8 are then driven to slide below substrates 2. By moving the holding poles 7 downward, transfer of the substrates 2 from the holding poles 7 to the holding poles 8 is possible.
It is understood that FIGS. 24 to 26 omit illustration of driving means for driving the chucks for clarity.
Although being capable of holding substrates, the conventional substrate holding devices discussed above create the following problems.
A problem encountered in the device of FIG. 24 is that the processing bath 50 must have a sufficient width to allow the chucks 1 to be opened wide enough to receive the substrates 2.
This directly counters the original intention of the carrier-less approach, i.e. to cut maintenance costs by reducing the sizes of processing baths and hence the amount of processing fluids. Thus, the device of FIG. 24 largely defeats the merits of the carrier-less approach.
On the other hand, the device of FIG. 25 is superior to the device of FIG. 24 in that the processing bath 50 can be narrower since the chucks 5 need not open so wide to engage and hold the substrates 2.
However, the guide grooves 6a cut in the holding plates 6 have a large overall area, and easily acquire and catch processing fluid therein and thus contaminate a successive processing bath.
Although the contamination is prevented by rinsing the chucks 5 sufficiently in a cleaning bath, a large amount of cleaning fluid is necessary for satisfactory cleaning. Hence, increase in maintenance costs is inevitable.
Further, the substrates 2, being clamped in the chucks 5 by the holding plates 6 and hence under clamping pressures from the two sides toward their centers, are likely to be damaged on the rims.
In the device of FIGS. 26A-26C, further size reduction of the processing bath is achieved since the necessity of providing chucks for holding the substrates is eliminated, and hence, the processing bath needs not to be so wide to allow insertion of the chucks. Thus, the device of FIGS. 26A-26C is superior in that its processing bath is the smallest among the above three processing baths.
Another important advantage is that the device of FIGS. 26A-26C sees less chance of contamination. One reason is because the holding action of the substrates 2 does not require immersion of the holding poles 8 into the processing bath. The other reason is that the total area of the guide grooves 8a is smaller than that of the corresponding guide grooves of FIG. 25.
These advantages in the device of FIGS. 26A-26C are, however, outweighed by disadvantages. The substrates 2 could fall down on or drop off from the holding poles 8 during the horizontal transportation thereof since the substrates 2 are supported only from below by the three holding poles 8, which makes it difficult to convey the substrates 2 at a high speed. In addition, it is necessary to provide different vertical driving means to travel up and down the holding poles 7 for different processing baths, thereby inviting design complexity.